1. Technical Field of the Invention
This invention relates to a semiconductor device and method for manufacturing the same.
2. Description of the Prior Art
In order to reduce a semiconductor chip thickness, conventionally the back-surface grinding process has been carried out to grind a back surface of a semiconductor wafer after having formed devices and interconnections (hereinafter, referred to merely as a xe2x80x9cwaferxe2x80x9d). The back-surface grinding process has been carried out by bonding a soft protection film on a wafer surface and pressurizing the wafer via the film to urge the wafer at its back surface onto a grid stone so that the wafer is rotated in that state.
However, the wafer or chip is handled by a robot in a process after grinding, i.e. in a process to cut a wafer into chips or a process to mount the cut chip onto a leadframe. Accordingly, thickness reduction, if excessively pursued, leads to wafer or chip breakage during handling, thus resulting in yield. In particular, in the present when wafer diameter has increased, there is a fear of readily breaking a wafer having a thickness reduced by back-surface grinding.
In order to solve such a problem, there is a proposal, e.g. by JP-A-11-150090 that projection electrodes are formed on a wafer surface and thereafter a resin layer is formed on the wafer surface to use the resin layer as a protection reinforcing plate. In the manufacturing method of a semiconductor device in the laid-open publication, wafer back-surface grinding is carried out after forming a resin layer and a surface layer of the resin layer is removed by etching, thereby exposing projection electrode summits. Thereafter, the resin layer is removed along the scribe lines. Furthermore, a nitride film as a protection film is formed in an area avoiding the projection electrodes. Thereafter, the wafer is cut along the scribe lines, into individual chips.
In this method, the wafer ground at its back surface is reinforced by the resin layer and also the individual chips cut from the wafer are reinforced by the resin layer. Due to this, the wafer and chip can be handled favorably without breakage. Meanwhile, such a chip can be mounted by connecting the exposed projection electrodes onto the electrodes pads of a circuit board or the like. Accordingly, it is possible to conspicuously reduce the semiconductor device thickness as compared to the structure with connection from an external terminal by the use of a bonding wire or the like.
However, in the manufacturing method of the foregoing prior related art, there is a problem of causing a warp in a wafer due to a difference in thermal expansion/contraction ratio between the wafer and the resin layer in a course of forming a resin layer on a wafer back surface to back surface grinding, as exaggeratedly shown in FIG. 4. In case such a warped wafer is ground with a flat grid stone, the wafer after grinding has a difference in thickness at between a wafer center area and a peripheral area. Accordingly, it is impossible to obtain semiconductor chips in an even thickness. In addition, there is a fear that the semiconductor chips cut from a wafer peripheral region be not thickness-reduced to a thickness as expected.
Accordingly, it is an object of the present invention to provide a manufacturing method making it possible to overcome the above-mentioned technical problems and favorably carry out a back-surface grinding process of a semiconductor substrate by preventing a warp in the semiconductor substrate, thereby suitably manufacture a thickness-reduced semiconductor device.
Another object of the invention is to provide a semiconductor device having a structure easy to reduce the thickness.
The present invention for resolving the problem is a method for manufacturing a semiconductor device including: a step of forming at least one of a projection electrode and an interconnection on one surface of a semiconductor substrate; a step of forming a resin layer on the one surface of the semiconductor substrate; a grinding process for polishing or grinding the other surface of the semiconductor substrate thereby reducing a thickness of the semiconductor substrate; and a process of forming a cut groove in the resin layer after the process of forming a resin layer but before the grinding process.
It is preferred to carry out the resin-layer forming process and cut-groove forming process with such a brief time spacing as not to cause a problem of a warp in a semiconductor substrate (wafer), or place a resin-layer-formed semiconductor substrate in an temperature controlled environment so as not to cause a large warp in the semiconductor substrate due to a difference in thermal expansion/contraction ratio between the semiconductor substrate and the resin layer before forming a cut groove in the resin layer.
According to the invention, because a cut groove is formed in the resin layer formed on one surface of the semiconductor substrate, no warp is caused due to a difference in thermal expansion/contraction between the semiconductor substrate and the resin layer. This makes it possible to evenly grind a back surface of the semiconductor substrate in a flat state of the semiconductor device. Accordingly, with such a method of manufacturing a semiconductor device, it is possible to obtain a semiconductor substrate having a thickness desirably adjusted. Namely, the semiconductor substrate obtained is evenly thickness-reduced in both a center area and a peripheral area. By cutting the semiconductor substrate into individual semiconductor chips, obtained are thickness-reduced semiconductor chips having an even thickness.
The cut groove is preferably provided in two or more directions (e.g. orthogonal two directions) in order not to cause a warp in any direction on a plane within the semiconductor substrate.
The resin layer is preferably formed covering summits of the projection electrodes or interconnections. Meanwhile, the resin layer preferably has a flat surface. In such a case, the semiconductor substrate can be evenly pressurized at a side formed with the resin layer during grinding. Because the semiconductor substrate or chip after grinding is covered, at its surface, with the resin layer and hence reinforced with protection, there is no fear of breaking the semiconductor substrate or chip during handling thereof. The projection electrodes or interconnections can be exposed at their summits by carrying out a process to remove a surface layer of the resin layer. This process may be by a chemical process such as etching or by a physical process such as grinding.
In the case of exposing the summits of the projection electrodes or interconnections by a physical process such as grinding, the summits of the projection electrodes or interconnections are flush with a surface of the resin layer. Due to this, after carrying out a process to expose the summits of the projection electrodes or interconnections, the semiconductor substrate can be evenly pressurized at one surface to carry out a grinding process on the other surface. Namely, such a semiconductor substrate has a freedom in the order of the processes to be made during manufacture.
The cut grooves may reach the semiconductor substrate or be formed in a depth of within a thickness of the resin layer. Meanwhile, the cut grooves are preferably formed along scribe lines formed to represent boundaries of between individual semiconductor devices on the semiconductor substrate. In this case, obtained is a semiconductor device including: a semiconductor substrate; a resin layer formed on one surface of the semiconductor substrate; and at least one of a projection electrode and an interconnection formed on the one surface of the semiconductor substrate; whereby the semiconductor substrate and the resin layer have, as cut surfaces, side surfaces at least one surface of which is a multi-staged cut surface obtained by cutting twice or more. A step is formed at a boundary between a cut surface formed upon forming the cut groove and a cut surface formed upon scribing.
The multi-staged (usually, two-staged) cut surface may be obtained through cutting the resin layer and part of the semiconductor substrate due to forming a cut groove and thereafter cutting the remaining part of the semiconductor substrate by scribing. Otherwise, the multi-staged cut surface may be obtained through cutting a part of the resin layer due to forming a cut groove and thereafter cutting the remaining part of the resin layer and semiconductor substrate by scribing. Namely, the step in the multi-staged cut surface may be in a region of the resin layer or region of the semiconductor substrate.
The number of cut grooves can be arbitrarily determined as long as the stress applied in the semiconductor substrate is fully reduced. In the case that cut grooves are formed along scribe lines, they may be formed along every scribe line. For example, cut grooves may be formed in a ratio of one per a predetermined number of scribe lines. Where cutting grooves are formed in a ratio of one per two scribe lines in each of orthogonal two directions, a semiconductor chip obtained has multi-staged cut side surfaces for the not-opposed two surfaces, and surfaces cut once upon scribing for the other two side surfaces.
In the case of forming cut grooves along all the scribe lines, the semiconductor chip has multi-staged cut surfaces in all the side surfaces. In case of forming cut grooves in a ratio of one per three or more scribe lines, obtained are semiconductor chips in a plurality of kinds of forms, e.g. those having a multi-staged cut surface only in one of the side surfaces, those having multi-staged cut surfaces in two of the side surfaces, and so on.
The semiconductor chip cut from the semiconductor substrate can be mounted by connecting an exposed part of the projection electrode or interconnection directly onto an electrode pad of a circuit board.